- (void)mouseDown:(NSEvent*)event

{

  NSLog(@"%s",__FUNCTION__);

  // if there is an image to drag around...

  if ( [self image] != NULL ) {

    // generate a file name, path, and url

    NSString *fileName = [NSString stringWithFormat:@"%@-%@",

        [[NSProcessInfo processInfo] globallyUniqueString],

        @"dragfile.png"];

    NSString *filePath =

        [NSTemporaryDirectory() stringByAppendingPathComponent:fileName];

    NSURL *fileURL = [NSURL fileURLWithPath:filePath];

    // create a temporary file to house the image

    CGImageDestinationRef destination = CGImageDestinationCreateWithURL(

        (__bridge CFURLRef) fileURL, kUTTypePNG, 1, NULL);

    if ( destination != NULL ) {

      CGImageDestinationAddImage(destination, [self image], nil);

      if ( CGImageDestinationFinalize(destination) ) {

        // add a reference to the file path to the drag pasteboard

        // using the special NSFilenamesPboardType type

        NSPasteboard *dragPasteboard =

            [NSPasteboard pasteboardWithName:NSDragPboard];

        [dragPasteboard declareTypes:@[NSFilenamesPboardType] owner:nil];

        [dragPasteboard setPropertyList:@[filePath]

            forType:NSFilenamesPboardType];

        // calculate the drag image and position

        NSImage* dragImage = [[NSWorkspace sharedWorkspace]

            iconForFile:filePath];

        NSPoint dragPosition = [self convertPoint:[event locationInWindow]

            fromView:nil];

        // perform the drag operation

        // this method call runs synchronously

        // so we can delete the file after it is

        // compete

        [self dragImage:dragImage

            at:dragPosition

            offset:NSZeroSize

            event:event

            pasteboard: dragPasteboard

            source:self

            slideBack:YES];

        // the above dragImage method runs synchronously, so when we return

        // here the drag operation is technically complete, the receiver will

        // have been called, etc.... However, some receivers will only have

        // made note of the drag operation and they may not be finished

        // with the file just yet so it's important not to delete it right away.

        // In this sample we maintain the file on disk for a short time

        // before deleting it.

        const uint64_t kSecondsToKeepFile = 3, kNanosecondsPerSecond = 1000000000;

        dispatch_queue_t mainqueue =

            dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

        dispatch_time_t when =

            dispatch_time(0, kNanosecondsPerSecond*kSecondsToKeepFile);

        dispatch_after(when, mainqueue,

          ^{  NSError *error;

            if (![[NSFileManager defaultManager] removeItemAtPath:filePath error:&error]) {

              NSLog(@"error removing %@ %@", filePath, error);

            }

          });

      }

      // done with the image destination

      CFRelease(destination);

    }

  }

}